Accrued Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accrued Liabilities
Accrued liabilities	$ 747	$ 687
Revenue payable [Member]
Accrued Liabilities
Accrued liabilities	86	94
Accrued capital costs [Member]
Accrued Liabilities
Accrued liabilities	332	231
Accrued lease operating expenses [Member]
Accrued Liabilities
Accrued liabilities	84	86
Employee incentive expense [Member]
Accrued Liabilities
Accrued liabilities	46	61
Accrued interest on debt [Member]
Accrued Liabilities
Accrued liabilities	46	52
Taxes payable [Member]
Accrued Liabilities
Accrued liabilities	116	122
Other accrued liabilities [Member]
Accrued Liabilities
Accrued liabilities	$ 37	$ 41